This application is the U.S. National Phase under 35 U.S.C. xc2xa7371 of International Application PCT/JP98/05192, filed Nov. 18, 1998.
The present invention relates to a method of manufacturing a multilayer wiring board having tow or more wiring layers. More specifically, this invention relates to a method of manufacturing a multilayer wiring board having the step of after forming a column-like metallic body on a lower wiring layer, forming an upper wiring layer whose part is conductively connected with the column-like metallic body.
In recent years, as electronic equipment and the like are miniaturized and light-weighted, electronic parts are miniaturized and the density of wiring boards to which the electronic parts are mounted is required to be high. In order to heighten the density of the wiring boards, a method of heightening line density of wiring layers or a method of obtaining a multilayer structure by laminating a plurality of wiring layers are adopted.
The method of manufacturing a multilayer wiring board includes a joining method of forming wiring layers respectively on a plurality of substrates and joining the substrates in a state that insulating sheets intervene between the substrates, and a build-up method of forming insulating layers on a substrate on which a wiring pattern is formed and forming the wiring pattern on an insulating layer, namely, of forming a laminated structure by repeating formation of an insulating layer and a wiring pattern.
In the multilayer wiring board, conductive connection between the wiring layers should be carried out according to a circuit design. For this reason, the build-up method of electrically connecting different wiring layers through a via hole ins adopted. This method will be explained with reference to FIG. 5.
Copper foils are formed on a surface of a substrate 1, and a pattern is formed on a first wiring layer 2 (see FIG. 5(1)) by a photo-lithography method. A photo resist or the lie is applied to the first wiring layer 2 so that an insulating layer 3 is formed (see FIG. 5(2)). Next, a mask 4 where a via hole pattern is formed is overlapped and exposure 5 and image development are carried out so that concave section 6 which reaches the first layer pattern is formed (see FIG. 5(4)). A copper thin film 7 and a copper plating film 8 are formed inside the concave section 6 by electroless copper plating and electrolytic copper plating (see FIGS. 5(5) and 5(6)). Thereafter, the copper plating film 8 is patterned to form a second wiring layer 10 and a via hole 9 (see FIG. 5(7)). This step is repeated to form more layers in the wiring board.
As a method of manufacturing a simple and low-priced printed-wiring board, Japanese Patent Application Laid-Open No. 6-314878 (1994) discloses a method of after forming a column-like conductor on a lower wiring layer, forming an upper wiring layer so as to conductively connect the wiring layers. This method will be explained below with reference to FIG. 6.
A conductive thin film layer 12 is formed on a surface of a substrate 11 by sputtering or the like (see FIG. 6(1)), and a pattern is formed thereon by electrolytic copper plating using a plating resist or the like (see FIG. 6(2)). Next, a plating resist is uniformly applied thereto, and exposure and image development are carried out so that a resist pattern 14 which is opposite to a via hole is formed (see FIG. 6(3)). Thereafter, while conducting with the conductive thin film layer 12, copper is deposited on a concave section 15 of the resist pattern 14 by electrolytic copper plating so that a copper column-like body 16 corresponding to a via hole is formed (see FIG. 6(4)). The resist pattern 14 is peeled and an exposed part of the conductive thin film layer 12 is removed by etching (see FIG. 6(5)). An insulating resin 17 is applied to the whole surface (see FIG. 6(6)), and this surface is heated and pressurized and flattened by a press apparatus so as to be flush with a height of the copper column-like body 16 (see FIG. 6(7)).
However, in this method, the height of the copper column-like body becomes non-uniform easily. Since electrolytic plating is carried out in a hole, bubbles are generated, causing a problem in that current density is not heightened, and it takes a long time to form the copper column-like body. Further, the formation of a resist pattern requires a complicated step such as laser emission or the like. As a result, this method is not advantageous from the view point of the cost.
Therefore, it is an object of the present invention to provide a simple and low-cost method of manufacturing a multilayer wiring board where a column-like metallic body having a more uniform height can be formed in a short time.
The above object can be achieved by the following present invention. Namely, a method of manufacturing a multilayer wiring board having the step of after forming a column-like metallic body on a lower wiring layer, forming an upper wiring layer whose part is conductively connected with the column-like metallic body, characterized in that the column-like metallic body is formed by the steps, comprising
(a) the step of coating the lower wiring layer with a conductor showing durability at the time of etching metal composing the column-like metallic body so as to form a conductive layer;
(b) the step of forming a plating layer of the metal composing the column-like metallic body on a whole surface including the conductive layer;
(c) the step of forming a mask layer on a surface portion of the plating layer where the column-like metallic body is formed; and
(d) the step of etching the plating layer.
According to the present invention, when the plating layer is formed previously on the whole surface at step (b), since the height of the portion where the column-like metallic body is formed is approximately uniform, the column-like metallic body having approximately uniform height can be formed. Moreover, at step (b), since the plating layer is formed not in a hole but on the whole surface, the plating layer having a desired thickness can be formed for short time with high current density, and the whole step time can be shorted. Further, at the step (c), since the mask layer is formed not on the whole surface having a hole but in a scattered point form, it can be formed by a simple and low-priced method such as printing.
As a result, the method of manufacturing a multilayer wiring board, which can form the column-like metallic body having uniform height for short time according to the simple and low-priced method, can be provided.
At the step (a), conductive paste (conductive coating) or the like can be used. However, it is preferable that the step (a) separates out the metal, which shows durability at the time of etching the metal composing the column-like metallic body, on the lower wiring layer according to electroless plating in which the metal composing the lower wiring layer is used as catalyst so as to form the conductive layer. As a result, the conductive layer can be formed selectively on the wiring layer, and a protective film having high etching resistance can be formed as the conductive layer by the simple method.
At this time, it is preferable that the metal composing the column-like metallic body is copper, and the conductive layer is made of nickel-gold alloy or tin-lead solder alloy. These alloys can be selectively plated by using copper as a catalyst and shows high durability at the time of etching copper. As a result, they can be used suitably as the metal composing the conductive layer.
In addition, as for the formation of the mask layer, various methods using dry film resist, organic compound type resist, metal resist or the like can be adopted. However, the printing method is preferable. In the present invention, since the mask layer is formed in scattered point form, the printing method can be adopted. As a result, the mask layer can be formed by the simple and low-cost step.
Meanwhile, the multilayer wiring board of the present invention is a multilayer wiring board which is manufactured by one of the above manufacturing methods. Since the column-like body in the multilayer wiring board is formed by etching after panel plating, a defect hardly occurs, and the lower wiring layer can be conductively connected with the upper wiring layer with high reliability.